1. Field of the Invention
The present invention relates to a switch structuring a network, and more particularly to an electronic switch.
2. Description the Related Art
Most switches arranged in a network are electronic switches these days. A software program describing capabilities required for a switch is installed in an electronic switch, and a switching process is implemented by executing this program. Depending on the description of the program, the electronic switch not only interconnects subscribers, but also can provide various additional services such as a three-party call, a call transfer, a centrex service, etc. As an example, the centrex service (Centralized Extension Service) is briefly explained below.
The centrex service is a service with which a station switch (a switch operated by a common carrier) is used as a PBX (Private Branch Exchange). Assuming that subscribers A and B enroll in the centrex service, the numbering system or the charge for the communications between the subscribers A and B is processed as those of an extension call. That is, once the extension numbers of these subscribers are registered to the switch beforehand, the switch recognizes that the extension number is the number assigned to the subscriber B, and connects the subscriber A to the subscriber B when the subscriber A dials the extension number of the subscriber B. At this time, the switch does not charge for this communication.
To implement the above described centrex service, the program describing a process for determining whether or not a calling party and a called party are enrolled in the centrex service, a process for converting an extension number into a number used in a normal communication, a process for preventing a charging counter from incrementing its value if a communication is the centrex communication, etc. the data required for the centrex service, etc. may be stored in the switch.
In this way, the electronic switch can provide various services (including additional services) depending on a program to be installed, etc.
As described above, a service provided by an electronic switch (simply referred to as a switch hereinafter) which structures a network is controlled by a program installed in each switch (switching node). That is, a physical node accommodating a subscriber and a node implementing a service is the same.
However, if a plurality of types of switches exist in a network, the types of services to be supported may differ depending on the types of switches. For example, one switch provides a three-party call service and a call transfer service other than the centrex service, while another switch provides all of the three services.
Accordingly, if a certain subscriber desires a service which cannot be provided by the switch currently accommodating the subscriber, the subscriber and the switch providing the desired service must be connected. Namely, the connection of the subscriber line must be changed. If these two switches are accommodated in an identical station building (for accommodating switches), the connection of the subscriber line can be changed by changing the connection in an MDF (Main Distribution Frame). However, if the switch providing the service that the subscriber desires is arranged in a different station, it is substantially impossible to change the accommodation of the subscriber line. This means that the subscriber cannot receive his or her desired service.
Furthermore, there is the demand for making subscribers accommodated by different switches belong to an identical centrex group. Such a system is generally called a City-Wide centrex service. The City-Wide centrex service is currently implemented with one of the following methods.
(1) Using the capability of an IN (Intelligent Network). With this method, the City-Wide centrex service can be provided to an arbitrary subscriber, but some restriction may be imposed on services which can be provided due to the restrictions of the IN signalling method.
(2) Arranging a switch dedicated to the centrex service. With this method, the switch dedicated to the centrex service must be arranged, and also a remote concentrator for connecting a subscriber to the switch dedicated to the centrex service must be arranged in each station building accommodating other switches. The subscriber who is to receive the centrex service is accommodated in a remote concentrator in the nearest station building, so that the subscriber is connected to the switch dedicated to the centrex service. With such a configuration, the subscribers accommodated by different station buildings are recognized to belong to the identical centrex group, and can receive services without any restrictions. With this method, however, a switch for accommodating a normal subscriber and a remote concentrator for connecting the centrex subscriber to the switch dedicated to the centrex service must be arranged together. Therefore, the equipment efficiency deteriorates, the equipment cost becomes expensive, etc.
Additionally, if a normal switch enters into an overload state, its load is reduced by restricting call origination or call termination (especially restricting the call origination). Accordingly, the quality of a service to be provided by a switch degrades, a call is difficult to be established during the restriction, etc.
An object of the present invention is to improve the quality of a communication service. More specifically, the object of the present invention is to allow a subscriber to receive his or her desired service provided by a switch which does not physically accommodate the subscriber without changing the connection of a subscriber line.
A switch according to the present invention assumes a first switch arranged in a network where a plurality of switches including the first and second switches are interconnected. The switch according to the present invention comprises a virtual access network device for making the second switch perform the process of a communication related to a subscriber accommodated by the first switch; a storing unit for storing attribute information indicating whether or not the subscriber accommodated by the first switch uses the virtual access network device; and a subscriber accommodating unit for accommodating an arbitrary subscriber among subscribers accommodated by the first switch in the virtual access network device based on the attribute information stored in the storing unit.
With this configuration, only a registered subscriber is accommodated in the virtual access network device. If one subscriber is accommodated in the virtual access network device, the process of the communication related to that subscriber is performed by the second switch. That is, the subscriber accommodated by the virtual access network device is accommodated in the first switch physically, but it is accommodated in the second switch substantially. Therefore, this subscriber can receive a service provided by the second switch.
A switching system according to the present invention assumes the configuration where a plurality of switches including the first and second switches are interconnected. The first switch comprises a virtual access network device for making the second switch perform the process of a communication related to a subscriber accommodated by the first switch; a storing unit for storing attribute information indicating whether or not the subscriber accommodated by the first switch uses the virtual access network device; and a subscriber accommodating unit for accommodating an arbitrary subscriber among subscribers accommodated by the first switch in the virtual access network device based on the attribute information stored in the storing unit. The second switch controls the communications related to subscribers accommodated by the virtual access network device.